Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

370
FXUS63 KLOT 301128
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
628 AM CDT Thu Apr 30 2026

.KEY MESSAGES...

- A generally cool pattern will prevail with occasional
  opportunities for scattered showers.

&&

.DISCUSSION...
Issued at 128 AM CDT Thu Apr 30 2026

Broad upper-level troughing remains in place across the Great
Lakes. Meanwhile, a broad surface high pressure system is
currently meandering through the middle Mississippi River
Valley. The combination of the weak pressure gradient and modest
upper-level subsidence in the wake of a departing upper-level
shortwave has allowed for mostly clear skies and nearly calm
winds early this morning. With temperatures falling into the mid
to upper 30s by daybreak, suppose there could be patchy frost
especially near the Wisconsin state line where readings will be
coolest. Also, will have to watch for patchy shallow ground fog
toward daybreak, particularly across northeastern Illinois where
dew point depressions are within a degree or two.

Today looks pretty similar to yesterday. Partly cloudy skies a
northwesterly breeze will lead to highs in the mid to upper 50s.
Another lake breeze will hold lakeshore locations to the upper
40s. The next upper-level shortwave pinwheeling around the broad
cyclonic flow is evident in GOES-19 water vapor imagery moving
into the Dakotas, and will move into the region this evening.
Steepening mid- level lapse rates by virtue of mid-level cold
aid advection will support scattered showers from the evening
through the first half of the overnight period with a higher
coverage expected today compared to yesterday. With forecast
soundings depicting the centroid of instability from 0C to about
minus 15C, would not be surprised to see a few instances of
graupel and perhaps evening a lightning strike in the deepest
cores.

Tonight looks similar to tonight with clearing skies and chilly
temperatures. With clearing taking place largely during the
overnight hours (as opposed to before), overnight lows will be
coldest and in the mid 30s across the northwest and modestly
warmer in the lower 40s southeast. Again, some patchy frost may
develop where temperatures are coldest (near the Wisconsin state
line).

Another shortwave (or two) may move into the region on Friday,
supporting another diurnal flare of showers. At this point,
indications are that instability will be more muted on Friday
compared to this evening, so will hold with "silent" 10 percent
chances for showers. With a large onshore component to the wind,
highs on Friday will be the chilliest of this stretch and range
from the upper 40s lakeside to mid 50s well inland (Mendota to
Gibson City).

Ensemble guidance continues to indicate that the aggregate
upper-level troughing will shift eastward this weekend and
beyond, placing the Great Lakes in broad upper-level
northwesterly flow. As a result, a line of shortwaves will be
poised to parade over the region leading to periodic
opportunities for showers and a few thunderstorms. Modest
warming may take place as well, particularly in the warm
advection regimes ahead of each wave. Looking well beyond, am
seeing a growing signal (particularly in EPS data) for another
shot for somewhat chilly air in the Thursday/Friday timeframe of
next week followed by a more definitive warming trend into the
middle of May.

Borchardt

&&

.AVIATION /12Z TAFS THROUGH 18Z FRIDAY/...
Issued at 628 AM CDT Thu Apr 30 2026

Forecast concerns include...

Chance of showers this afternoon into this evening.
Lake breeze/wind shift to northeast this afternoon.
Chance for mvfr cigs overnight/Friday morning.

Areas of fog mainly south of the terminals and near GYY will
quickly dissipate this morning.

Light west/northwest winds will slowly increase this morning
and will shift northeasterly this afternoon with a lake breeze.
Only medium confidence for timing and trends will need to be
monitored. Winds are expected to turn back to light northwest
later this evening. There is another potential shift back to
north/northeast with a frontal boundary Friday morning. Added
the northeast directions to the ORD/MDW 30 hour tafs, but low
confidence at this time.

A weak disturbance will move across the area this afternoon into
this evening bringing scattered showers. Expected coverage
continues to increase and have changed prob to tempo mention.
Showers may linger into this evening before ending.

Guidance is trending lower with cigs overnight into Friday
morning with low mvfr cigs possible. Confidence is low but
introduced scattered mention for now. cms

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

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